Umar Farouk Abdulmutallab, pictured with a woman believed to be a family member, defended the Taliban in class. Photo: MIKE RIMMER

The suspect was on an intelligence database but was not on the government's no-fly list, meaning he was known to authorities but not considered a high risk Photo: AP

A Northwest Airlines passenger from Nigeria, who said he was acting on al-Qaida's instructions, set off an explosive device Friday in a failed terrorist attack on the plane as it was landing in Detroit

Security sources believe that Umar Farouk Abdul Mutallab, 23, may have developed links with other extremists during the three years he spent studying at University College London.

The Security Service is concerned that the son of a respected Nigerian banker was "off the radar" while living in Britain from 2005 to 2008 on a student visa.

Little more than a year later he went on to attempt a terrorist attack after being trained by al-Qaeda. Officers are trying to track his movements and activities while in the country amid suspicions that he may not have acted alone.

Mutallab was under heavy guard in hospital after his failed attempt to set off a bomb on a passenger jet containing 278 passengers and 11 crew as it came in to land in Detroit, Michigan, on Christmas Day.

They suspect that he had planned to launch the attack from Britain but was stopped after being refused a student visa earlier this year to study at a college that was judged to have been bogus.

The MI5 investigation came as:

President Barack Obama ordered a review of US screening measures after it emerged that Mutallab was put on a "watch list" of terrorist suspects in November but was not included on a "no-fly" list that would have stopped him from flying into the US.

Tens of thousands of air passengers in Britain faced lengthy delays and confusion following the introduction of increased security on flights to the US.

Concerns were raised about the student visa system that allowed Mutallab to stay in Britain for three years. Whitehall officials have expressed fears previously that extremists were exploiting lax rules.

MI5 and the Metropolitan Police Counter Terrorism Command have drafted in extra staff to search for any links Mutallab may have to radicals. Sources said it was not Britain that supplied the information that led to Mutallab being put on the US "watch list".

"We have not come up with anything but we are now going back through our work to see if he may have been on the periphery of another group or trying to contact radicals in this country," said one.

"We need to know what he was doing in the UK and whether he was just a student. There may be some fragment that we come across that sheds some light on that."

Mutallab’s attack raises questions about the operations of intelligence agencies on both sides of the Atlantic. British security officers will need to explain why they remained unaware of a would-be terrorist living in London for three years.

Earlier this year, Jonathan Evans, the head of MI5, suggested that al-Qaeda cells in Britain were being forced to "keep their heads down" due to the success of the service’s operations.

The attempted atrocity will also prompt concerns in the US that Britain is increasingly being used as a base by Islamic extremists planning attacks overseas.

In Washington, US officials are already under pressure to explain why the threat posed by Mutallab was not taken more seriously and why alarm bells did not ring when he paid for his ticket in cash and did not check in any luggage.

Embassy officials in Nigeria, who had been warned of Mutallab’s behaviour by his father, were accused of not wording their warning more strongly. Janet Napolitano, the head of the Department of Homeland Security, said "there had never been any additional information supplied that would move him to a secondary list".

On Sunday, as US prosecutors charged Mutallab with attempting to blow up the Northwest Airlines Airbus, fresh details emerged of the plot.

He has told the FBI that al-Qaeda provided the bomb materials and training after he made contact with a cell in Yemen. He bought a ticket for almost $3,000 and, carrying a US visa issued in London last year, returned to Nigeria on Dec 24.

He flew to Schipol airport in Amsterdam and transferred to the flight to Detroit.

Mr Obama asked for a review of security and screening procedures after it emerged that Mutallab used explosive materials similar to those used in December, 2001, by Richard Reid, the so-called shoe bomber.

His device included PETN, one of the ingredients of the plastic explosive Semtex, but got through security in Nigeria and Holland. He had allegedly hidden the powder in a condom strapped to his inner thigh along with a syringe of liquid to mix with it.

It is thought that he assembled the device in the lavatory after complaining to fellow passengers about a stomach upset. It ignited but did not explode, merely causing a small fire that was extinguished by the crew as other passengers leapt on Mutallab.

Mutallab lived with relatives in a West End apartment while studying at UCL but cut off ties with his family after he graduated. He moved to the Middle East and then to Yemen, sending a text message last August warning them that they may not see him for a number of years.

There was another alert last night after a second plane was forced to make an emergency landing at Detroit. The pilot raised the alarm after a Nigerian on the flight from Amsterdam locked himself in the lavatory for up to an hour. He was eventually dragged out after crew broke down the door, but no explosives were found

The family of a former London student accused of trying to blow up a transatlantic jet have said they alerted security agencies two months ago after losing contact with him.

Umar Farouk Abdul Mutallab's parents describe his disappearance as "completely out of character" and a "very recent development", in a statement.

Meanwhile, Barack Obama has ordered an urgent review of airport screening after Mutallab allegedly tried to destroy an airliner headed to the US on Christmas Day.

Investigators are trying to find out how the 23-year-old Nigerian evaded security checks to board the plane, which was carrying 278 passengers.

Authorities had apparently been warned about Mutallab's extremist views by his own millionaire father.

A spokesperson for the Obama administration said the probe targeted the Department of Homeland Security, specifically the Transportation Security Administration.

He said the US President was "interested in learning how the explosive material was brought on board the aircraft and steps that can be taken to enhance the ability of airport screeners to detect and interdict such materials in the future".

Mr Obama has also demanded a report into how watch-lists on terror suspects are used following reports that Abdul Mutallab's name was included on one before the Christmas Day incident.

He was apparently listed on the Terrorist Identities Datamart Environment list, which contains more than a million names, many of them only tangentially linked to terror suspects.